mlxsw: reg: QEEC: Add minimum shaper fields

Add QEEC.mise (minimum shaper enable) and QEEC.min_shaper_rate to enable
configuration of minimum shaper.

Increase the QEEC length to 0x20 as well: that's the length that the
register has had for a long time now, but with the configurations that
mlxsw typically exercises, the firmware tolerated 0x1C-sized packets.
With mise=true however, FW rejects packets unless they have the full
required length.

Fixes: b9b7cee4 ("mlxsw: reg: Add QoS ETS Element Configuration register")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>